1. Field of the Invention
The present invention relates to an unsaturated polyester resin composition and a cured resin thereof. Particularly, it relates to an unsaturated polyester resin composition and a cured resin thereof preferably used for molding a reflecting mirror base of a vehicle lamp such as a head lamp or a fog lamp mounted in an automobile, and relates to a lamp reflecting mirror base made of the cured resin.
2. Description of the Related Art
A thermoplastic resin such as an unsaturated polyester resin has been used widely in a field of home building materials such as wall materials, floor materials, bathtubs, dressing tables, tiles or artificial marble; a field of ships; a field of automobiles; or an electric and electronic field. A reflecting mirror of a lamp such as a head lamp or a fog lamp mounted in an automobile in the automobile field needs to endure high heat generated from a filament in use because a very high luminance electric bulb with the filament is used in combination with the reflecting mirror. Hence, a lamp reflecting mirror base is made of a thermoplastic resin composition excellent in heat resistance. For example, a composition for molding a lamp reflecting mirror has been disclosed in Japanese Patent Laid-Open No. 28442/1982. The disclosed composition is prepared in such a manner that a low-shrinkable unsaturated polyester resin composition containing 10 to 25% by weight of glass fiber, and 50 to 65% by weight of filler such as calcium carbonate is mixed with calcium stearate chemically bonded to the filler as a miscible internal lubricant and an aliphatic peroxy compound as a curing agent.
Although a lamp reflecting mirror, particularly a lamp reflecting mirror preferably used in a head lamp mounted in an automobile, needs to have heat resistance and strength to endure high heat (about 180° C.) generated at the time of switching on the lamp, a lamp reflecting mirror using the low-shrinkable unsaturated polyester resin composition disclosed in Japanese Patent Laid-Open No. 28442/1982 as a base material may be thermally deformed because of increase of heat in a lamp chamber at the time of switching on the lamp when the lamp reflecting mirror is used for a long time. It has been also found that both dimensional stability and surface smoothness are spoiled because the base material is shrunk by heat generated at the time of injection-molding the lamp reflecting mirror base.
As a result, a surface of the reflecting mirror is distorted. The distortion causes roughening of the reflecting mirror surface, so that light irradiated from the electric bulb cannot be controlled accurately. Hence, there is a problem that a light distribution standard cannot be satisfied or dazzling light may be given to a car coming from the opposite direction.